Ala. Code § 40-1-44

(a) Interest shall be added as provided herein to any tax or other amount due the department which is not paid by the due date. Interest on any delinquency shall be charged from the due date of the tax, except (1) interest on delinquent license taxes levied under Chapter 12 of this title shall be charged from the delinquent date provided in subsection (e) of Section 40-12-10; and (2) interest on delinquent license tax and registration fees levied on motor vehicles shall be charged beginning after the period allowed for registration or renewal; and (3) interest on the freight lines and equipment companies tax levied in Section 40-21-52 shall be charged from the delinquent date thereof. The interest shall be computed based on the underpayment rate established by the Secretary of the Treasury under the authority of 26 U.S.C. §6621.

(b)(1) Except as provided in subdivision (2) of this subsection (b), interest shall be paid by the department on any refund of tax erroneously paid directly to the department. Interest shall be computed on any overpayment from the date of overpayment to the department; except, a. interest on any refund resulting from a net operating loss carryover or carryback shall be computed from the date the claim giving rise to the refund is filed, b. interest on any overpayment of tax withheld and paid over to the state pursuant to Article 2 of Chapter 18 of this title and estimated tax paid pursuant to Section 40-18-83, shall be paid beginning 90 days after the due date of the return required by Section 40-18-27 for individuals, and Section 40-18-39 for corporations, or the date the return is filed, whichever is later. Interest as required above shall be computed at the same rate as provided herein for interest on underpayments.

(2) No interest shall be paid on any overpayment of the following taxes:

a. Taxes paid by entities for which a refund is allowed by Sections 40-9-12 and 40-9-13;

b. License taxes which are refunded pursuant to Sections 40-12-23 and 40-12-24;

c. Gasoline taxes paid on gasoline used for agricultural purposes for which a refund is allowed by Division 3, Article 2, Chapter 17 of this title;

d. Gasoline taxes paid on gasoline used for the static testing of engines for which a refund is allowed by Division 4, Article 2, Chapter 17 of this title;

e. The motor fuels excise tax levied by Section 40-17-141 for which a refund or credit is allowed by Section 40-17-142;

f. The tobacco taxes levied by Chapter 25 of this title; and

g. The motor fuels excise tax levied under the Alabama Terminal Excise Tax Act, which has been paid to a supplier by a licensed distributor or end user who is authorized to obtain a refund under Section 40-17-329, if the refund is paid within 90 days of the receipt of the proper documentation.